package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;


public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或返回结果过多");
        }
    }

    @Override
    public int insert(String statementid, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        int result = simpleExecutor.insert(configuration, mappedStatement, params);

        return result;
    }

    @Override
    public int update(String statementid, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        int result = simpleExecutor.update(configuration, mappedStatement, params);

        return result;
    }

    @Override
    public int delete(String statementid, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        int result = simpleExecutor.delete(configuration, mappedStatement, params);

        return result;
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        //使用JDK动态代理来为Dao接口生成代理对象并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            /**
             * 代理对象调用接口中的任意方法，都会执行invoke()方法
             *
             * @proxy 当前代理对象的引用
             * @method 当前被调用方法的引用
             * @args 传递的参数 user
             */
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable, Exception {
                //底层都还是去执行JDBC代码 //根据不同情况，来调用selectList或者selectOne
                //准备参数1：statementid：sql语句的唯一标识：namespace.id = 接口全限定名.方法名
                //方法名：findAll
                String methodName = method.getName();
                //接口全限定名
                String className = method.getDeclaringClass().getName();

                String statementId = className + "." + methodName;

                //准备参数2：params：args
                //获取被调用方法的返回值类型
                Type genericReturnType = method.getGenericReturnType();
                //判断是否进行了 泛型类型参数化:当前返回值类型是否有泛型，如果有泛型就是集合，没有就是实体
                if (genericReturnType instanceof ParameterizedType) {
                    List<Object> objects = selectList(statementId, args);
                    return objects;
                }
                if (method.getName().equals("insert")) {
                    return insert(statementId, args);
                }
                if (method.getName().equals("update")) {
                    return update(statementId, args);
                }
                if (method.getName().equals("delete")) {
                    return delete(statementId, args);
                }
                return selectOne(statementId, args);
            }
        });
        return (T) proxyInstance;
    }

}
